"It's heartbreaking to see more innocent civilians being killed in Gaza, this time in a UN-run school.

"If the two sides of this conflict, both Hamas and Israel, need any further reminding of how tragic this conflict is, and how it will lead to nothing, it will just lead to more senseless violence, then I think we've seen that evidence overnight.

"I plead with both sides to stop, and stop now."

UN Secretary-General Ban Ki-moon angrily denounced the Gaza attack and said the killing must "stop now".

He said: "Many have been killed - including women and children, as well as UN staff.

"Circumstances are still unclear. I strongly condemn this act."

The fighting during the conflict has left at least 803 Palestinians dead and injured more than 5,000 [REUTERS]

US Secretary of State John Kerry pushed for a ceasefire as he met Egypt's foreign minister and Mr Ban in Cairo.

Israeli media said the country's Security Cabinet had unanimously rejected the proposal for a temporary pause in the Israel-Hamas fighting.

A US official later said that Israeli Prime Minister Benjamin Netanyahu told Mr Kerry that Israel will begin a 12-hour pause in Gaza hostilities starting tomorrow.

The Israeli government did not immediately comment on the report.

Violence spread to the West Bank last night, with thousands of Palestinians who were protesting against the Gaza fighting clashing with Israeli soldiers near Ramallah.

At least one Palestinian was killed and dozens were injured, a Palestinian doctor said.

Earlier this week the UN's top human rights official Navi Pillay condemned both Israel's military actions and those of Hamas.

She added that Mr Netanyahu's country may have perpetrated "war crimes" during their bombardment of Gaza.

Ms Pillay said: "There seems to be a strong possibility that international law has been violated, in a manner that could amount to war crimes."